Signaling system



Sept. 18, 1928. 1,684,445

R. K. HONAMAN SIGNALING SYSTEM Filed July 12, 1926 ATTORNEY PatentedSept. 18, 1928. V

PATENT OFFFCBQ RICHARD K. I-IONAMAN, OE BLOOMFIELD, NEW JERSEY, ASSIGNORTO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEWYORK.

' SIGNALING SYSTEM.

Application .filed July 12,

This invention relates to signaling systems, and particularly toarrangements in such systems for minimizing noise.

In hi h frequency transmission systems, such as radio broadcasting andcarrier systems, in which a carrier frequency modulated by low frequencysignals is transmitted, noise currents having frequencies Within therange used for transmission .are introduced into the transmitting mediumand give rise to noise at the receiving station of the system. Thisnoise results mainly from the beating of the carrier frequency by thenoise currents introduced into the transmitting me dium. Under certainconditions, the components of the noise currents, which are within thelimits ofaudibility, are easily heard at the receiving station.

Duringintervals in a broadcasting program of news, music, or the likewhen no low frequency signals are modulated on the carrier frequency,as, for example, during the quiet intervals in the program, noise ofthis nature is particularly objectionable because of the fact that thenoise stands out during these intervals. On the other hand, duringperiodsv in the program when the low frequency signals are modulated onthe carrier frequency, the noise may be submerged by these low frequencysignals.

As stated above, noise becomes audible at the receiving station duringthe quiet inter-v vals in the program, and results from the interactionof the carrier frequency andthe noise currents introduced into thetransmitting medium from extraneous sources. Cer-. tainly, if thecarrier frequencycan be cut off during these quiet intervals, the noisewill be greatly reduced, rendering these intervals substantially quietat the receiving station. Furthermore, the carrier frequency serves nouseful purpose during these ,quiet intervals.

It is therefore an object of this invention to provide arrangementssuitable for transmitting a carrier frequency when there are lowfrequency signals oriother modulating energy to be modulated thereon,and for substantially suppressing the carrier frequency when there areno such low frequency signals or other modulating energy to be modulatedthereon. v

While the nature of the invention will be pointed out withparticularityin the ap, pended claims, the invention itself, both as toits further objects and features, will be 19% Serial no. 122,016.

better understood from the detailed description hereinafter followingwhen read inconnection with the accompanying drawing, in which Figure 1represents one embodiment of the invention, and in which Fig. 2represents a characteristic curve of a vacuum tube showing theinterrelation of plate current an (1. grid voltage.

In F 1, there is shown a transmitter S, or other source of low frequencysignals, ar ranged in a series circuit with a battery B, and the primarywinding of a transformer T The transformer T connects the circuit of thesource of lowfrequency signals S to a duplex modulating" system having.two three-element.thermionic tubes M and M each havinga filament, a gridand a plate, the filaments being heatedto an electron-emittingtemperature b r a common battery. The tubes M and M, are preferablysimilar and equal in their structure and characteristics, and certainlymay be replaced by a single duplex tube having a single filament, twogrids and two plates; The input circuits of these tubes if, and M arearranged in parallel with respect to the secondary winding oftransformer T which winding is in series with a battery B in the commonconductor of the input circuits of these tubes. .The secondary oftransformer T consists of two windings which may, for example, be woundin the same direction, one in the input circuit of the tube M andtheother in the input circuit of the tube-M,.- The output'circuits of thesetubes are also-connected through the primary windings of a transformer Tin parallel with respect to a common-plate battery B The secondarywinding of transformer T is connected to an output circuit-O.

The primary winding of the. transformer T has a generator G connectedthereto, which generates, for example, the carrier frequency to beemployed in the system. By virtue of the connection between thegenerator G and the transformer T the grids of the tubes M and M arebothin phase with respect to the carrier frequency transmitted bygeneratorG. The oscillations of the carrier;frequencywill therefore beimpressed in the same directions on the input circuits of these tubes,and under normal conditions the grids of these tubes will be equallybiased negatively by battery Equal currents therefore flow in the outputcircuits of the tubes M and M but these currents are oppositely directedby the 7 it will have a very high transmitter primary windings of thetransformer T Consequentlyythese currents effectively balance andneutralize each other, rent flows in the output circuit 0. r p

In formerarrangements of duplex translating circuits, when low frequencysignals were generated at the source S, the grid of one of the tubes Mor M became positive while the grid of the other tube became negative,so that the resistance of one tube decreased while the resistance of theother increased. This then caused an'increase in the current fiowing'inthe output circuit of the tube in which the grid became positive and acorresponding decrease in the current flowing in the output circuit ofthe tube in which the grid-becanienegative. The tubes M and M wereactuated only when low frequency signals were impressed on the grids ofthese tubes; i

The resent inventioncomprises arrangements or substantially suppressingthe carrier frequency of the generatorG when'no low frequenc signals aretransmitted bythe S and-for transmitting the carrier frequencyof'thegenerator G modulated by the low frequency signalstransmitted bytheltransmitter S'whensuch signals are generated. :A neon tube N,orother discharge device, is accordingly connected in the inputcircuit-of one of the tubes, M This neon tube has abreakalown potentialwhich is abovethe potential of the battery B lVhen the potential acrossthe terminals of the neon tube is less than its break-down potential,impedance, and when thenpotential'across'the terminals of the neon tubeis'equal to, or less than, its breakdownpotential, it will have amoderate impedance. -Because of this 'factvthe neontube will beineffective in the system until 'the potentialacross itstermin'als isgreater than its break-down potential. And until thi-s'break-downpotentialis applied to the terminalsof the neon'tube N, t ierewill bepractically no effective current flowingin the primary windings of thetransformer T and consequently no current will be transmitted'totheoutput circuitO.

The neon tube N 's so arranged in the systerm that when low frequencysignals are transmittedby'the source S, a potential will be generatedacross'the terminals of theupper windingofthetransformer T so that thecumulative potential of the batter B and that generated across thetermina s of the'upper secondary winding of-the transformer T will begreater than the breakdown potential of-the neon 'tubeN. When thisoccurs currentwill flow'from the battery B through theneon tube N in alocalcircuit whichincludes the battery B the upper secondary Winding ofthe transformer T a resistanceR and the neon'tube N. The

neontube N willthereforeshunt the grid and no cur-' and filamentof thetube M so thatthe grid of the tube M will not be biased negatively asmuch as the grid of the tube M Consethe primary windings of thetransformer T,,'

are oppositely directed there will be a re- 'sultant carrier currenttransmitted to the secondary winding of the transformer T,, which willbe proportional to the difference between the'currents flowing in theoutput circuits of the tubes M and M respectively. The output circuit 0will therefore receive current of the carrier frequency modulated by thelow frequency signals.

The'neon tube N operates very'rapidl so that a change from the conditionin W iich carrier current is to be transmitted to the condition in whichcarrier current is to be suppressed takes. place practically instantly.Furthermoreyno change occurs in the structure of the neontube Nsuchaswill'interfere with its operating characteristics.

Fig. 2 showsa curve characteristic of the tubes M andfM in which gridvoltage .is plotted as abscissas against. plate current as ordinates.The point a on this characteristic curve has an ordinatewhichcorresponds to the average plate current in both. tubesli/I and M whenno low frequency signals are being transmittedto the grids of-thesetubes In a perfectly balanced system the current in'the plate circuit ofone of the tubes'will be equal to the current in the plate circuit ofthe other of the tubes. I

\Vhen the'low frequency signals are being transmitted'to the gridsofthese respective tubes. it has beenshown hereinabove that'the neontube N associated with the tube M shuntsthe grid and-filament of thetubeM 50 that the potential of the grid with respect to the'filament of thetube'M will no longer be equal to the potential of the rid with re-vspectto thefilamentof the-tu e M The grid of the'tubeM will be lessnegatively biased with respect to "its filament than it previously-was.The point b of the characteristic curve represents the point 'at which ithe tube M then operates. This point b is less negative than thepoint'a,andthereforethe plate current in the tube M is greater than the platecurrent in the tubeM Thelines drawn from the points aand b te the axisof abscissas correspond, respectively, to the plate currents in thetubes M and M l Consequently, the current in the secondary windingo'fthe transformer T receives 7 a carrier current having an amplitudeproportional to" the dif ference between these two lines.

It will be understood that by changingflthe magnitude of the potentialof the battery B the magnitude of the resistance R or the break-downpotential of the neon tube N, the amplitudeof the carrier currentflowing lun 7 high frequency wave by in the output circuit 0 may besuitably controlled. v

It will be understood also that while a neon tube has been shown anddescribed herein for the purpose of illustration, any other device whichhas a high impedance when the potential applied thereto is below apredetermined value and a moderate impedance when the potential appliedthereto equals, or is greater than, the predetermined value, may beemployed instead thereof within the scope of the appended claims. Whilethe arrangements of this invention have been shown and described in oneparticular embodiment merely for the purpose of illustration, it is tobe understood that the invention is capable of embodiment in other andwidely variedorganizations without departing from the spirit of theinvention and the scope of the appended claims.

What is claimed is:

1. The method-of signaling which consists in generating a high frequencywave, generating low frequency signals, modulating the high frequencywave by the low frequency signals, and substantially suppressing thehigh frequency wave when the magnitude of the low frequency signalsdrops below a predetermined value and freely transmitting the highfrequency wave modulated by the low frequency signals when the magnitudeof the low frequency signals rises beyond the predetermined value.

2. The method of signaling which consists in generating a high frequencywave, generating low frequency signals, modulating the the low frequencysignals, transmitting the modulated high he quency wave when themagnitude of the low frequency signals is above a predetermined level,and substantially suppressing the high frequency wave so that it remainsuntransmitted when the magnitude of the low freiluerlicy signals isbelow said predetermined eve 3. The method of signaling which consistsin generating an alternating current wave of one frequency, generatinglow frequency signals, superimposing said low frequency signals on saidalternating current wave, and substantially suppressing the alternatingcurrent wave when low frequencysignals are being generated below apredetermined level and freely transmitting the alternating current wavemodulated by the low frequency signals when the low frequency signalsare being generated above said predetermined leve 4:. The method ofsignaling which consists in generating a wave of one frequency,generating a wave of a second frequency, superimposing the wave of thesecond frequency on the wave of the first frequency, and substantiallysuppressing the wave of the first frequency when the wave of the secondfresignals, when quency is being generated at a level below apredetermined value andfreely transmit ting the wave of the firstfrequency modulated by the wave of the second frequency when the wave ofthe second frequency is' erator of a high frequency wave, a source oflow frequency signals, means for modulatng the high frequency wave bythe low frequency signals, means for transmitting the high frequencywave modulated by the low frequency signals when the energy level of thelow frequency signals is abovea predetermined value, and means forsubstantially suppressing the high frequency wave so that it remainsunmodulatcd and untransmitted when the energy level of the low frequencysignals is below the predetermined value.

7. A signaling system comprising a generator of an alternatingcurrent'wave, a generator of low frequency signals, means forsuperimposing the low frequency signals on the alternating current wave,and means for substantially suppressing the energy of the alternatingcurrent wave when the energy of the low frequency signals drops below apredetermined level and for freely transmitting the energy of thealternating current wave with the superimposed low frequency signalswhen the energy of the low frequency signals rises abovethepredetermined level.

8. A signaling system comprising a generator of current of onefrequency, a generator of current of a second frequency, means :forsuperimposing the wave of the second frequency on the Wave of the firstfrequency, and means for substantially suppressing the wave of the firstfrequency when the wave of the second frequency is being generated at alevel below a-predetermined value and for freely transmitting the waveof the first frequency modulated by the wave of the second frequencywhen the wave ofthe second frequency is being generated at a level abovethe predetermined value.

9. In a translating system, a pair of translating devices having inputand output circuits, a circuit for the reception of signal waves,another circuit containing a source of energy of a carrier wave, one ofsaid circuits being symmetrically associated with said input circuitsand the other being oppositely associated with said input circuits, atreceivpreventing the flow mg circuit diflt'erentially associated withsaid outputcircuits, and means for substantially of energy of thecarrier Wave tothe receivingcircuit when the level of theenergy of thesignal waves is below a-predetermined value and for freelypermitting theflow of energy of the carrier vvave modulated by energy of the signalwaves to the receiving circuit when the level of theenergy of the signalWaves is above the predetermined value. c

10. In a translating system, apair of translating devices having'inputand output circuits, a circuit for the reception of signal '11 Amodulating system comprising a pair of translating devices, a source ofhigh frequenc energy symmetrically connected with said evices, a sourceof modulating energy oppositely connected with said devices, 'an outputcircuit diflerentially connected with said devices, and means consistingof a discharge device connected to one of the translating devices forsubstantiall unbalancing the translating devices when'te modulatingimi-44c energy is normal, whereupon the output circuit will receive highfrequency energysuperimposed by modulating energy.

a '12. A modulating system comprising a pair of translating devices, asource ofhigh flquenc energy symmetrically connected-with said evices, asource of modulating energy oppositely connected with said devices, :anout oing circuit differentially connected wit said devices,andrmeansconsisting-eta discharge device connected to one of the translatingdevices for substantially vincreasing the flow of current a in a oneofsaid translating devices beyond'thatoccurring in the other of saidtranslating dev ces, whereupouthe outgoing circuit will; receive hi hfrequency energy superimposed by modu ating energy.

13. A modulating system comprising a pair ottranslating devices a sourceof'high -frequency energy symmetrically connected with said translatingdevices, a source ofi modulating energy oppositely connected with saidtranslating devices, a an outgoin circuit differentially connected withsa-i translating devices, and a discharge device connected to one ofsaid translating devices which vvillbe inefiective untiltheinodnlatingenergy rises beyond a predetermined value, whereupon theflow of current in the translatingdevice to which the discharge deviceis connected will substantially exceed the flow of current in the othertranslating (device. a i

"In testimony whereof, I-have "signed my name to. this specificationthis .lOth .day; of

July 1926. V V

RICHARD :K. ,HONAMAN.

